1. Field of the Invention
This invention relates to a lubricant-fuel mixture for two-cycle internal combustion engines in which the mixture has reduced smoke emission due to the presence of an amine salt and/or amide of a derivative of thiobenzoic acid.
2. Description of Related Art
In the last several years, the use of spark-ignited two-cycle internal combustion engines has increased significantly. This is due to their use in a variety of garden and recreational equipment such as motorcycles, marine outboard engines, snowmobiles, power mowers, snow blowers, chain saws, and the like. As such, the amount of smoke released from two-cycle engines has become a major environmental concern to engine manufacturers and fuel suppliers. However, few smoke reducing additives are commercially available, and the few that are contain metals, which are environmentally undesirable.
Amine salts of certain benzoic acid derivatives have been used as extreme pressure (EP) agents for water-based metal cutting fluids. For example, Japanese Patent No. 55023132 describes a water-based metal cutting fluid containing an EP agent comprised of an alkali metal salt, an ammonium salt, an amine salt, or an ester of a halogenated benzoic acid derivative such as hydroxy benzoic acid, alkoxy benzoic acid, alkyl benzoic acid etc. The EP agent is claimed to have excellent lubricating property, rusting resistance, and EP properties as compared with conventional nitrites typically used for water-based metal cutting fluids.
Substituted benzoic acids have also been used as EP agents in water-based fluids. For example, U.S. Pat. No. 4,569,776 discloses a water-based hydraulic fluid composition comprising substituted aromatic compounds like benzoic acids, aromatic sulfonic acids, phenyl alkyl acids and substituted benzenes. Examples of these compounds include mono-, di-, and triaminobenzoic acids; alkyl-substituted (C.sub.1 to C.sub.12 atoms) mono-, di-, and triaminobenzoic acids and mono-, di-, and trialkoxy (C.sub.1 to C.sub.12 atoms) benzoic acids.
U.S. Pat. No. 4,434,066 discloses a water based hydraulic fluid containing a combination of a hydroxyl-substituted aromatic acid component and a nitroaromatic compound component. Suitable acidic materials include saturated and unsaturated aliphatic carboxylic and polycarboxylic acids having at least six carbon atoms, aromatic carboxylic acids and alkali metal or organic amine salts of said aliphatic and aromatic acids.
U.S. Pat. No. 4,012,331 discloses a lubricating oil composition comprising a sulfur compound prepared by reacting a trithiolan compound with a thiol compound in the presence of a base where the thiol compound comprises thiophenol, thiosalicylic acid, thioacetic acid, thioglycolic acid, thiobenzoic acid, etc., including an amine or alkali metal salt thereof.
More recently, the use of the additives of this invention as an antioxidant in lubricating oils and as a flow improver in middle distillates has been disclosed in copending applications U.S. Ser. Nos. 582,316 and 545,002, respectively.
However, none of these publications suggest the particular additive for the two-cycle engine lubricant-fuel mixture disclosed herein or its effectiveness in reducing the smoke formed during combustion of the mixture.